Rotary coin mechanisms are widely used in merchandise-dispensing machines such as bulk venders for dispensing gum balls and other small articles. Such a vender accepts a coin of the intended denomination and as the handle is turned dispenses a preset volume of merchandise to the user. The handle is rotationally fixed to a rotating coin conveyor, which includes a coin recess in which the coin is conveyed about the rotational cycle of the mechanism. Upon rotation of the handle the coin recess rotates past one or more measuring devices that arrest rotation unless the coin is of the required size. If the coin is of the proper size, rotation continues past a dispensing position, the coin is released into a concealed coin tray and the coin conveyor returns to its rest position as the merchandise is dispensed. Such coin mechanisms are well known to those skilled in the art.
Bulk venders and other like apparatus provide a predetermined amount of space for the coin mechanism, and coin mechanisms are thus typically designed to fit all of the necessary parts into the smallest possible space. With the increasing variety of merchandise that such venders are capable of dispensing, and with cost increases due to inflation, it is frequently necessary to design the coin mechanism to accommodate a larger size of coin. In some currencies all coins within the desired nominal range are quite large. However, to accommodate a larger coin without changing the size of the coin mechanism it is necessary to enlarge the coin recess toward the axis of the coin conveyor, ie. toward the shaft of the handle. This considerably reduces the structural integrity of the coin conveyor, because the coin recess occupies most of the thickness of the coin conveyor leaving only a thin web of material to retain a coin in the coin recess. As the coin recess is enlarged toward the axis of the coin conveyor the amount of material surrounding the shaft in the region of the coin recess is commensurately reduced, ultimately to the point where the coin conveyor can no longer be reliably rotationally engaged to the shaft because a relatively small amount of torque becomes sufficient to split the coin conveyor hub. This is a significant problem, because the coin conveyor is the sole part of the mechanism which prevents the handle from being rotated, and thus merchandise from being freely dispensed, unless the correct coin is deposited into the vender.
A further problem arises through the continued use and abuse of coin mechanisms, due to the way the coin conveyor is conventionally mounted. Bulk venders are designed for self service by users, and as such are frequently placed in locations where their use cannot be readily supervised. As a result bulk venders are constantly subjected to attempts to steal merchandise. This frequently involves the use of slugs, or coins from other currencies with lower monetary value, and thus coin mechanisms have evolved with measuring devices that operate to high tolerances, to detect and reject coins or slugs varying in size from a coin of the intended denomination. Coin mechanisms can also be subjected to traumatic impacts in attempts to break the rotational lock and steal merchandise (known as "milking" the vender), which over time loosens the fit between the coin conveyor and the shaft, allowing the coin conveyor to shift radially relative to the shaft.
When the tolerance between the coin conveyor and the handle shaft is reduced due to wear and abuse, so that the coin conveyor can shift radially relative to the shaft, the effectiveness of the diameter measuring device is reduced because a coin will not necessarily follow a consistent rotational path about the mechanism. Even a slight eccentric misalignment of the coin conveyor on the shaft can cause the mechanism to malfunction, resulting in losses to the operator.